Acquired Inflammatory neuropathies are a considerable social and economic burden to our Veterans and to the Veterans Health Administration. Encompassing both known infectious or possibly infectious etiologies, inflammatory neuropathies constitute one of the largest and least understood spectrums of neurologic disorders. Inclusive among these disorders is acute inflammatory demyelinating polyradiculopathy (AIDP), a highly disabling inflammatory autoimmune disease of the peripheral nervous system that is characterized by acute/subacute symmetrical paresis with areflexia progressing to neuromuscular paralysis. Despite its overwhelming prevalence and socioeconomic impact, the treatment of Veterans with inflammatory peripheral neuropathies, including AIDP, remains palliative. Cytokine-mediated recruitment and trafficking of autoreactive leukocytes across the blood-nerve barrier and into peripheral nerves is a well-established early pathological hallmark of inflammatory peripheral neuropathies, including AIDP. Localized GTPase-dependent activation of the peripheral nerve vascular endothelium in response to proinflammatory cytokines represents an initiating pathological insult. Peer- reviewed and published preliminary studies from our laboratory strongly support that trafficking of autoreactive leukocytes into peripheral nerves during AIDP may proceed by a mechanism that involves Cdc42 GTPase- dependent secretion of CCL2. Novel translational studies are critically needed to develop therapeutic and rehabilitative strategies for the advanced care of Veterans debilitated by acquired inflammatory neuropathies. In this two-year SPiRE study, we will determine whether siRNA-mediated GTPase knockdown therapeutically protects against the development and progression of inflammatory neuropathy. Hypothesis: Therapeutically administered siRNA directed against key monomeric GTPases will attenuate the development and progression of experimental autoimmune neuritis by inhibiting endothelial cell CCL2 expression. This hypothesis will be tested in vivo with the following two Specific Objectives using an established clinically- translatable rat model of AIDP (experimental autoimmune neuritis, EAN). Specific Objective 1 will determine whether prophylactic or therapeutically administered siRNAs targeting key monomeric GTPases protects against the development and progression of EAN. We will determine the dose- dependent effect of siRNAs targeting Cdc42 or RalA GTPases on (a) the clinical severity and course of EAN and on (b) EAN-induced changes in peripheral nerve function, using evoked-response electrophysiology. Specific Objective 2 will determine whether prophylactic or therapeutically administered siRNAs targeting key monomeric GTPases attenuates trafficking of autoreactive leukocytes into peripheral nerves during EAN. We will (a) validate siRNA-mediated knockdown of key monomeric GTPases (Cdc42 or RalA) within sciatic nerves of siRNA-treated EAN rats, compared with scrambled siRNA-treated EAN controls, and (b) quantify the content and distribution of CCL2, CCR2, and immune infiltrates (macrophages and leukocytes) within sciatic nerves of siRNA-treated rats, compared with scrambled siRNA-treated EAN controls, with immunohistochemistry. The goal of this study is to establish siRNA-mediated Rho GTPase knockdown as a viable therapeutic strategy for the management of inflammatory peripheral neuropathies. We argue that successful completion of this study will expedite the translation of siRNA technology into mainstream management of Veterans with acquired inflammatory neuropathies, including AIDP.